Biological Sciences

Legislation in US and Europe has been adopted to determine the ecological integrity of estuarine and coastal waters, including, as one of the most relevant elements, the benthic macroinvertebrate communities. It has been recommended that greater emphasis should be placed on evaluating the suitability of existing indices prior to developing new ones. This study compares two widely used measures of ecological integrity, the Benthic Index of Biotic Integrity (B-IBI) developed in USA and the European AZTI's Marine Biotic Index (AMBI) and its multivariate extension, the M-AMBI. Specific objectives were to identify the frequency, magnitude, and nature of differences in assessment of Chesapeake Bay sites as 'degraded' or 'undegraded' by the indices. A dataset of 275 subtidal samples taken in 2003 from Chesapeake Bay were used in this comparison. Linear regression of B-IBI and AMBI, accounted for 24% of the variability; however, when evaluated by salinity regimes, the explained variability increased in polyhaline (38%), high mesohaline (38%), and low mesohaline (35%) habitats, remained similar in the tidal freshwater (25%), and decreased in oligohaline areas (17%). Using the M-AMBI, the explained variability increased to 43% for linear regression, and 54% for logarithmic regression. By salinity regime, the highest explained variability was found in high mesohaline and low polyhaline areas (53-63%), while the lowest explained variability was in the oligohaline and tidal freshwater areas (6-17%). The total disagreement between methods, in terms of degraded-undegraded classifications, was 28%, with high spatial levels of agreement. Our study suggests that different methodologies in assessing benthic quality can provide similar results even though these methods have been developed within different geographical areas. #

Climate impacts on coastal and estuarine systems take many forms and are dependent on the local conditions, including those set by humans. We use a biocomplexity framework to provide a perspective of the consequences of climate change for coastal wetland ecogeomorphology. We Estuaries and Coasts (2008) 31:477-491

A study was conducted to define winter distribution patterns of blue crabs, Callinectes sapidus, in the l o w e r Chesapeake Bay and to relate these patterns to environmental variation. During February 1986 a stratified random survey was conducted to examine the distribution of blue crabs with respect to three major habitat types: 1) high energy, wave-and tide-dominated, spits and shoals; 2) moderate energy, tide-dominated basins; and 3) variable energy, tide-dominated or quiescent channels (natural or cut). Each major habitat type was further stratified on the basis of location (to account for possible salinity effects), resulting in a total of 17 habitat-stratum combinations. Blue crabs exhibited significant differences in abundance among habitats. Crabs were most abundant in the basin habitat and least abundant in the shoal and spit habitat. A posteriori evaluations of abundance patterns in relation to sediment type and depth showed that crabs were significantly more abundant where sediments contained between 41 and 60% sand and at depths exceeding 9 m. The sampled population of blue crabs was dominated by mature females. T h e r e were no significant differences in crab sex ratios between habitats, but significant differences between two fixed sites sampled through the winter showed that there were p r o p o r t i o n a t e l y m o r e male crabs at the western site than there were at the eastern site. The observed patterns indicate that some differential habitat utilization occurs and that overwintering female crabs are found preferentially in areas characterized by moderate energy regimes and fine, but sandy sediments.

The study was designed to investigate ecological relationships among numerically dominant species of amphipods in the families Ampeliscidae and Corophiidae on the outer continental shelf of the Middle Atlantic Bight. USA. It assesses the importance of b i o t~c interactions by examining spatial and temporal patterns in abundance and distribution. A complex set of physical and biological factors govern distribution and abundance of these species within the outer shelf zone. In outer shelf swale (topographic depression) habitats the ampeliscid Ampelisca agassizi effectively excludes other members of the family. This may be the result of the species' superior ability to utilize spatial resources. Outside of swale habitats the abundances of the ampelisclds Ampelisca vadorum and Byblis serrata may be limited by the availability of trophic resources. The corophiids exhibited little evidence of resource partitioning. Some differences in microhabitat distribution may facilitate coexistence of the species in this family, as well as between families. The corophiids Unciola irrorata and Erichthonius rubricornis are known to comprise a major portion of the diet of benthic fishes on the outer shelf. It is suggested that populations of these species may be held below the levels at which biotic interactions become important by both benthic predators and physical disturbance.

proposed that temporal and spatial mismatches between eastern oyster filtration and phytoplankton abundance will preclude restored stocks of eastern oysters from reducing the severity of hypoxia in the deep channel of central Chesapeake Bay. We refute this contention by presenting arguments, data, and model results, overlooked by these authors. Our analysis indicates that oyster populations living on extensive reefs along the flanks of the mainstem Bay could substantially reduce summer phytoplankton growth and particulate organic carbon deposition to deep waters of the central channel. Because hypoxia in these deep waters is maintained through microbial decomposition of organic carbon generated by summer phytoplankton production, we conclude that reduced carbon fluxes to the deep channel associated with greatly increased oyster grazing could reduce the severity of hypoxia.

Low dissolved oxygen (hypoxia and/or anoxia) has become a major cause of change to the benthic component of ecosystems around the world. We present the response of a benthic community to hypoxia in organically enriched environments in Korean coastal waters. Disturbances due to low dissolved oxygen (DO), and organic enrichment altered community dynamics, result in defaunation during summer hypoxia with delayed recolonization occurring in winter. As DO decreased, the number of taxa, their abundance and biomass of macrofauna dropped significantly at inner bay stations in Chinhae Bay and Youngsan River estuarine bay affected by hypoxia. With the return of normoxic conditions in Chinhae Bay, recolonization was initiated by opportunistic species, with a 1-4 months lag. The polychaetes, Sigambra tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia, were most persistent under hypoxia. The first recolonizers were the polychaetes Paraprionospio pinnata, S. tantaculata, Glycinde gurjanovae and Nectoneanthes multignatha and the bivalve Theora fragilis. The second group of colonizers included the polychaetes Capitella capitata, Mesochaetopterus sp. and L. longifolia, and the bivalve Raetellops pulchella. Hypoxic and near anoxic conditions resulted in mass mortality in Chinhae Bay and Youngsan River estuarine bay, but communities did partially recover after return to normoxic conditions despite delayed recolonization.

Hopper dredging operations release suspended sediment into the environment by agitation of the bed and by discharge of overflow slurries. Monitoring of turbidity and suspended sediment concentrations in central Chesapeake Bay revealed two plumes: (1) an upper plume produced by overflow discharge and (2) a near-bottom plume produced by draghead agitation and rapid settling from the upper plume. The upper plume dispersed over 5.7 km 2 extending 5,200 meters form the discharge point. Redeposited sediment accumulated on channel flanks covering an area of 6.4 km2 and reached a thickness of 19 cm. Altogether dredging

Restoration of the oyster Crassostrea virginica population in Chesapeake Bay is often advocated as an easy solution for controlling phytoplankton blooms. Even at their pre-colonial densities, oysters are unlikely to have controlled blooms, despite the fact that sediment cores suggest that pre-colonial spring blooms were smaller than at present. Lack of access to all bay water and low springtime filtration rates would make it impossible for oysters to control the spring bloom and the resulting summer hypoxia. Previous studies have overestimated potential oyster filtration rates, because they extrapolated summer rates to spring conditions that are 20°C cooler. Previous studies have also assumed that oysters have access to all phytoplankton, without considering the spatial separation. In Chesapeake Bay, oysters and the spring bloom are separated horizontally owing to the size of the bay and its small tidal amplitude. Indeed, a multi-species guild of suspension feeders now present in the bay should have a filtration capacity approaching that of pre-colonial oysters, but it does not control the bloom. Actual oyster filtration potential must be lower than many advocates of oyster restoration assume, and replenishing the bay with oysters is not the means of controlling blooms and hypoxia.

Sediment erodibility was measured at three sites in the York River, a sub-estuary of the Chesapeake Bay, monthly to bimonthly from April 2006 through October 2007. Erodibility at the three sites was similar during the summer and fall. A site near the estuary mouth maintained this level of erodibility greater than 90% of the time while two sites in the more physically dominated mid-estuary region exhibited a consistent and pronounced increase in erodibility in the late winter and spring. Weak to non-existent correlations between bed erodibility, solids volume fraction, and surficial concentrations of organic matter, colloidal carbohydrate, and extracellular polymeric substances, were not sufficient to explain the observed seasonal pattern in bed erodibility. Digital X-radiographs revealed thick sequences (10-20+ cm) of laminated sediments at the surface in the middle estuary coincident with the period of highest erodibility and more biologically reworked sediment during the rest of the year, suggesting that periodic rapid deposition introduced new sediment that was seasonally easy to erode. The finding that seasonal deposition influenced erodibility at the mid-estuary sites is consistent with previous results indicating the occasional presence of a secondary turbidity maximum. Comparison of the biologically reworked, but still "low" erodibility condition in the York to other published Chesapeake Bay erodibility data revealed a consistent critical shear stress range and profile, suggesting that this equilibrium critical stress profile may be representative of other similar estuarine environments in the absence of rapid deposition. At relatively low stresses and in the absence of rapid deposition, we speculate that burrowing and/or pelletization may play a role in maintaining high equilibrium bulk water content without reducing the strength of the surface of the seabed.

We characterized the abundance and species composition of sessile and mobile epifaunal assemblages in the York River, a tributary of the Chesapeake Bay, U.S., during the summer hypoxia seasons in 1996 and 1997. We collected communities on artificial substrates in two areas of the river that have historically experienced different exposure to hypoxia. Despite frequent hypoxic stress, epifauna formed dense communities in both areas. Dominant species comprised a range of phyla and included the polychaetes Polydora cornuta and Sabellaria vulgaris, the bryozoans Membranipora tenuis and Conopeum tenuissimum, the tunicate Molgula manhattensis, the barnacle Balanus improvisus, the anemone Diadumene leucolena, and the hydroids Ectopleura dumortieri and Obelia bicuspidata. Common mobile species included the nudibranchs Cratena kaoruae and Doridella obscura, the amphipods Melita nitida and Paracaprella tenuis, the polychaete Nereis succinea, and the flatworm Stylochus ellipticus. We found few differences in species composition between the two areas, even though one area usually experienced lower oxygen concentrations during hypoxic events, suggesting that hypoxia does not exclude any epifaunal species in the York River. We did find differences between the two study areas in percent cover and abundance of some species. While tunicates, hydroids, and anemones were equally abundant in both areas during both study years, bryozoans and the polychaete S. vulgaris were more abundant in the area with generally higher oxygen, suggesting that they may be less tolerant of hypoxic stress. The polychaete P. cornuta was more abundant in the area that usually had lower oxygen. These results suggest that many epifaunal species have high hypoxia tolerance, and most epifaunal species found in the lower York River are able to survive in hypoxic areas. Epifaunal species are not necessarily more susceptible to hypoxia than infaunal species in the York River. Epifaunal communities in areas with brief hypoxic episodes and moderate hypoxia (0.5-2 mg O 2 l Ϫ1 ) can persist with little change in species composition, and with few changes in abundance, as oxygen concentrations fall.

The York River Estuary, a tributary of the Chesapeake Bay, USA, experiences periodic low Ž . oxygen stress hypoxia , yet epifaunal species form dense communities there. We studied hypoxia tolerance of common epifaunal species in the York River by exposing sessile and mobile epifauna to high and low oxygen concentrations in laboratory aquaria. Mortality in hypoxia varied among species, ranging from 0% to 100%, with trends of decreased tolerance by mobile species relative to sessile species. While most species tested experienced some mortality after being exposed to Ž . Ž . hypoxia at 1 mg O rl or 0.5 mg O rl for 5 days, many species had a median lethal time LT 2 2 50 ) Corresponding author. L.C. Schaffner . 0022-0981r01r$ -see front matter q 2001 Elsevier Science B.V. All righst reserved. Ž . PII: S 0 0 2 2 -0 9 8 1 0 1 0 0 2 2 0 -9 ( ) A. Sagasti et al.r J. Exp. Mar. Biol. Ecol. 258 2001 257-283 258 epifaunal communities might be through its indirect effects on behavior and predation. q

The population structure, growth and production of the trigonal clam Tivela mactroides were investigated by monthly sampling between January 2003 and October 2004 in two areas (southern and northern) of the intertidal and subtidal zones of Caraguatatuba Bay, Southeastern Brazil. Intertidal sampling was carried out in each area along eight transects perpendicular to the shoreline. In the subtidal zone of both areas, one 50-m dredging was performed along five sampling stations arranged on three transects perpendicular to the coast. The intertidal abundance of T. mactroides was higher in the southern (more dissipative conditions) than in the northern area. High abundances occurred in February-March 2004 in the south and in September 2004 in the north. The size structure showed that younger individuals dominated in the sublittoral, indicating that recruitment occurs in this zone, followed by the migration of these individuals to the intertidal, where they complete their life cycle. Tivela mactroides showed continuous reproduction, with 26 cohorts detected in the study period. The lower estimates for the growth index (/′ = 3.22), mortality rate (Z = 2.10 year À1 ) and turnover rate (P/B = 1.21 year À1 ), and conversely the longer life span (2.5 years) of T. mactroides in Caraguatatuba Bay (24°S) compared with Venezuelan populations (10°N) suggests a latitudinal pattern of these life-history traits. The high production of T. mactroides in Caraguatatuba Bay was due to continuous recruitment and rapid and continuous growth, and demonstrates the importance of T. mactroides as a biological resource for many marine species and for the local residents.